The invention relates to a string trimmer/mower apparatus and more particularly to rotating trimmer head of a string trimmer/mower apparatus having at least one plate with a line retaining device, and further to a stack of such plates that provides a plurality of vertically spaced line retaining devices enabling cutting height adjustment by selectively securing a length of cutting line to one of the plates.
String trimmers, for example, hand held trimmers, two wheeled trimmers and even four wheeled trimmers or mowers have been used for cutting vegetation with lines that are secured to a rotating head driven by an engine or motor. Typically, such string trimmers have been used for cutting the areas of vegetation that are inaccessible to mowers having steel blades. However, recently string trimmers have gained acceptance in the cutting of vegetation, e.g. grass, in a wide variety of situations.
For cutting vegetation with a string trimmer along an edge of a walkway or fence, for example, the vegetation is usually cut very close to the ground. As another example, however, string trimmers have been used as lawn mowers to cut grass at a desired length above the ground, for example two to four inches in order to provide a cut having a neat appearance. Still further, string trimmers have found wide use in the cutting of field-type growth that is cut rather infrequently and that is left at a height of three to five inches or even more. Therefore, various designs have been incorporated in string trimmer heads to secure the string at a fixed height above the ground to select the height of the cut.
Also, many types of line retaining devices have been developed for use with string trimmers. With respect to retaining the cord on the trimmer head, it has been recognized that the cord or line experiences significant centrifugal force in operation of the trimmer. Further, as the cutting cord engages the vegetation, it is subjected to stress and vibration that will break the cord. While addressing these problems, other problems have resulted from designs attempting to provide a cord retaining arrangement which securely retains the cord on the trimmer head.
In several types of rotating trimmer heads, a length of flexible cutting line is secured to a disk using a clamping arrangement. For example, McGrew, U.S. Pat. No. 4,726,176, discloses a cutter for a rotary lawn mower in which radially extending passages between a central recess and the periphery of the disk are provided for accepting a length of cutting line. In this arrangement, the ends of the cutting line are fed into each of two passageways from the central portion of the disk. This leaves an intermediate portion remaining in the central recess of the disk that is clamped by the nut or bolt that holds the cutter on the drive shaft.
In another arrangement, shown in Dees, Jr. et al, U.S. Pat. No. 5,836,227, lengths of cutting line are held in channels of a lower plate which has an upper plate clamped down on the lower plate to secure the cutting lines in position within the channels. Altamirano et al, U.S. Pat. No. 5,862,655, shows yet another example, wherein a rotating cutting head has strings secured to the periphery of the disk using channels along the periphery of the trimmer head for the line. In this arrangement, the line is clamped by a plate bolted to the trimmer head to secure the lines in place.
In each of the above-described cutting heads of the prior art, it is necessary to clamp the line in place once the line has been fed into a channel or passageway. Clamping of the line is not desirable, however, since it requires an extra assembly step to be performed each time the line is replaced. Briar, U.S. Pat. No. 4,068,376, discloses an example of a cutter head that does not require a clamping arrangement. The rotating cutter head has an entry opening and an exit opening along the periphery of the disk through which a cutting line passes. One end of the cutting line is fed into the entry opening so that it passes through a connecting passageway and out the exit opening. The other end of the cutting line has an enlarged tab that prevents the line from passing through the entry opening and to ensure that the cutting line is secured by centrifugal force during the rotation of the cutting head. The cutter head of Briar, therefore, requires that the operator use specially designed cutting line that is precut into lengths wherein a tab is added to each line, which is undesirable.
Rouse, U.S. Pat. No. 4,756,146, also discloses a line retaining device that secures the cutting line without clamping the line to secure it. In this patent, a fixed line trimmer head is disclosed in which pairs of passages are located on the periphery of the head, each having entry and exit openings. Between each pair of the passages is a land. In use, the ends of a length of line are pushed through the entry openings of the passages on opposite sides of the land. When the ends of the line exit the passages, an intermediate portion of the line is engaged against the land thereby retaining the line. This enables the line to be replaced without unclamping the disk, however, the forming of the passageways requires assembling together two overlying disk-like plates that have matching recesses. Further, a ground engaging portion or ball is formed as an integral projection of the lower plate thereby preventing any cutting height adjustment from being made between the passageways that hold the line and the ground. Accordingly, although the line can be secured without the need for a clamping arrangement, the design of the trimmer head does not readily permit adjustments to be made to the cutting height.
Lack of adjustment in cutting height is a common problem. In each of the aforementioned patents, the trimmer head does not provide height adjustment. Rather, the distance between the ground engaging part of the trimmer head (if so equipped) and the cutting plane or line retaining disk in which the cutting lines emerge is not readably adjustable.
On the other hand, in Smith et al, U.S. Pat. No. 5,661,960, adjustment of the height between the body or platform of the line trimmer and the cutting lines is adjustable using spacer plates. However, there is no ground engaging structure for the trimmer head, so the distance between the cutting lines and the ground cannot be adjusted using the spacer arrangement. As a result, the two wheel line trimmer of Smith et al is typical of the prior art in which the operator adjusts the cutting height by balancing the position of the trimmer over the ground using the handles. This leads to uneven cutting unless a ground engaging member is used with the trimmer head.
The cutting height of prior art trimmers that use a ground engaging member can be adjusted by changing the distance between the ground engaging member and the cutting lines. Typically, however, this height cannot be adjusted without using tools or disassembling the trimmer head assembly and substituting various parts that provide a different spacing or distance between the plane in which the cutting line rotates and the bottom most part of the ground engaging member that moves across the ground during cutting. For example, trimmer/mowers are known that have a trimmer head in which the line is held by a plate that is mounted on a hub. The plate is vertically adjustable by loosening a set screw that locks it in position on the hub. The TROY-BILT trimmer/mower, for example, uses such an arrangement. Accordingly, adjustment of the cutting height of trimmer/mowers, in general, requires the use of tools or disassembly and assembly steps that deter the operator from making quick adjustments that otherwise might be preferred.
It is an object of the invention to overcome the above mentioned drawbacks of the prior art string trimmer designs. In particular, it is an object of the invention to provide a string trimmer apparatus that has a rotating head in which the cutting line can be replaced and securely retained without the need for making adjustments with tools, without the requirement for disassembly and assembly of the trimmer head, and in particular without the need to clamp the cutting line in place.
It is an object of the invention to provide a trimmer head having a plurality of axially or vertically spaced apart line retaining devices for enabling cutting height adjustment of the plane in which the string or line emerges from the trimmer head in a string trimmer apparatus without the need for making the height adjustment with tools or for disassembling the trimmer head to make the height adjustment.
It is a further object of the invention to provide a string trimmer head having at least two plates, each of which has at least one line retaining device, that are arranged in a stack. To adjust the cutting height, the cutting line is secured to one or the other of the plates using the respective line retaining device(s).
According to a preferred embodiment of the invention, each plate of a stack of line retaining plates has a predetermined thickness so that the respective line retaining devices are spaced apart from one another in suitable vertical increments for cutting height adjustment. In this regard, spacers can be added to the stack of plates to provide additional spacing or the stack can be formed of a plurality of plates that are substantially the same. Further, the cutting line can be secured to one or more line retaining devices of only one of the plates at a time, or to more than one of the plates at a time, as the situation requires.
It is yet a further object of the invention to provide a plate for a string trimmer head having at least one cutting element retaining device to which a cutting element, such as a length of line or string, is secured without the need for tools or for a clamping arrangement to secure the line in place. Depending on the circumstances, one plate can be used for providing the function of securing a line to the trimmer head. Optionally, the line retaining plate can be used in conjunction with other plates or a ground engaging member, in the assembly of a trimmer head when cutting height adjustment is not required.
It is still a further object of the invention to provide a plate for a string trimmer head having a cutting element retaining device, in which the plate is able to be stacked with like or different plates to form a stack of plates that substantially forms the trimmer head, optionally with a ground engaging member. Spacer plates can be incorporated in the stack to space the respective cutting element retaining devices apart from one another or the thickness of the plates can provide an inherent spacing function. The height of cutting can be adjusted by selectively using an appropriate plate for retaining the cutting element at the desired height or, alternatively, a cutting element can be secured to each plate for providing cutting at plural heights at the same time.